This invention relates to apparatus and method for spraying liquid from an aircraft such as utilized in agricultural aircraft for spraying fields and for fire fighting purposes.
Characteristically such aircraft demand high horsepower to perform the various close manueverings associated with agricultural spraying or fire fighting. It is thus important that the power required for spraying of the liquid not place a significant parasitic load on the engine. Certain prior art has attempted to solve this problem by developing the power for the liquid spraying system independent of the engines through a propeller or fan separately exposed to the surrounding airstream. Such a propeller does of course induce a continuous drag on the aircraft and thus must still be carefully designed, etc. to minimize drag. Also, limited control of the spraying system results, and/or significant complication is introduced into its control system, since this powering system is totally dependent upon the airstream flowing past the aircraft and is variable with aircraft air speed. Examples of such types of liquid spraying systems may be found in U.S. Pat. Nos. 2,924,040; 3,061,247; 3,351,305; and 3,455,511.
Another concept for aircraft liquid spraying system centers around utilization of a compressed air source directly or indirectly provided by the aircraft propulsion engine. The compressed air is fed to an accumulator-type reservoir for liquid to be sprayed, the air pressure directly forcing the liquid through the nozzle spray system. The potential energy storage characteristics of such an accumulator tends to reduce the peak power drained from the propulsion engine. However, significantly limited controllability of the liquid being sprayed is evident in such systems. Examples of this type of spraying system may be found in U.S. Pat. Nos. 3,494,423; and 3,774,871. Other less pertinent spraying systems may be found in U.S. Pat. Nos. 3,547,000 and 3,362,643.